Patent Document 1 discloses a technique having a valve opening/closing timing control apparatus (referred to as a “variable valve timing apparatus” in the above document) for setting opening/closing timings of an intake valve and an exhaust valve simultaneously. With this, the technique provides a control according to which when an engine load is below a predetermined value, closing timings of both the intake valve and the exhaust valve are retarded with maintaining an overlap between the intake valve and the exhaust valve constant.
Patent Document 2 discloses a technique having a valve opening/closing timing control apparatus (referred to as an “intake timing varying mechanism” in the above document) for setting an opening/closing timing of an intake valve and a valve opening/closing timing control apparatus (referred to as an “exhaust timing varying mechanism” in the above document) for setting an opening/closing timing of an exhaust valve, and a center timing of an overlap between the intake valve and the exhaust valve is varied according to a load.
Further, Patent Document 3 discloses a technique according to which an overlap when both an intake valve and an exhaust valve are opened simultaneously is set and through adjustment of an amount of this overlap, an internal EGR suitable for an operational condition of an internal combustion engine is obtained. This Patent Document 3 is characterized in that the overlap amount is set based on a guide value corresponding to an operational state of the internal combustion engine.